Numerical Modeling Study on Mineral Alteration and Sealing Performance for CO2 Geological Sequestration with Enhancing Water Recovery in Hydraulic Fractured Shale Reservoirs

Recently, CO2 geological sequestration combined with enhancing deep saline water/brine recovery is regarded as a potential strategic choice for reduction of CO2 emissions. This technology not only achieves the relatively secure storage of CO2 which was captured during industrial processes but also can enhance the recovery of water for drinking, industrial, and agricultural utilization. However, the impact of CO2-water-rock reactions on the shale reservoir in the system is unclear and the sealing performance of mudstone caprock has not been investigated. For analyzing the mechanism of mineral alteration in the shale reservoir, a three-dimensional injection-production model in the double-fractured horizontal well pattern is established according to actual parameters of shale and mudstone layers. In addition, mineral alteration was characterized and caprock sealing performance was also assessed. Numerical results showed that the presence of CO2 can lead to the dissolution of k-feldspar, oligoclase, chlorite, and dolomite and the precipitation of clay minerals such as kaolinite, illite, and smectite (Ca-smectite and Na-smectite). Due to positive ion released by dissolved primary minerals, the precipitation of secondary carbonate occurs including ankerite and dawsonite, which induces the mineral sequestration capacity of the shale reservoir. The amount of CO2 sequestration by mineral is 51430.96 t after 200 years, which equals 23.47% of the total injection (219145.34 t). Besides, the height of the sealing gas column is used for evaluating the sealing performance of the shale-mudstone interface. Results show that the height of the sealing gas column at the interface above the injection well is lower but the maximum value of CO2 gas saturation is only 0.00037 after 200 years. The height of the sealing gas column at the interface is greater than 800 m, which can be classified as level II and guarantee the security of the CO2 storage. The analysis results provide reliable guidance and reference for the site selection of CO2 geological sequestration.

Study of the Long Term Acid Gas Sequestration Process in the Borzęcin Structure: Measurements Insight

Geological sequestration of acid gases, including CO2, is now a growing solution to prevent progressive Earth climate change. Disposal of environmentally harmful greenhouse gases must be performed safely and securely to minimise leakage risk and possible uncontrolled emissions of injected gases outside the sequestration structure. The paper describes a series of research activities at the Borzęcin sequestration site located in western Poland, which were designed to study the migration paths of injected acid gases (mainly mixture of CO2 and H2S) into the water-bearing layers underlying natural gas reservoir. Along with understanding the nature and dynamics of acid gases migration within the sequestration structure, the research was also addressed to assess its leak-tightness and the long-term safety of the entire reinjection facility. As a part of the research works, two downhole sampling campaigns were completed in 2018–2019, where samples of water underlying the Borzęcin reservoir were taken and subsequently studied to determine their physicochemical parameters that were never before examined. Compositions of gas dissolved in downhole brine samples were compared with produced and injected gas. Relevant studies of reservoir water from selected wells were performed, including isotopic analyses. Finally, four series of soil gas analyses were performed on the area surrounding the selected well, which are important for the hazardous gas sequestration safety analysis in the Borzęcin facility. All the above mentioned research activities aimed to acquire additional knowledge, which is valuable for risk assessment of the acid gas sequestration process taking place on the specific example of the Borzęcin site operating continuously since 1996.

Optimal Selection of Favorable Areas for CO2 Geological Storage in the Majiagou Formation in the Ordos Basin

<p>CO<sub>2</sub> geological storage (CGS) technology is currently one of the best choices for large-scale low-cost CO<sub>2</sub> emission reduction in the world, and the primary issue of CO<sub>2</sub> geological storage is the optimization of the selection of favorable areas for CO<sub>2</sub> storage. In view of the insufficient research on the optimization of favorable areas for CO<sub>2</sub> geological storage in the Majiagou Formation in the Ordos Basin, this study aims to determine the boundaries of the CO<sub>2</sub> geological storage area in the Ordos Basin by studying the temperature and pressure conditions, reservoir conditions, structural conditions, caprock conditions , and the salinity conditions of the formation water using a large amount of geological, drilling, geophysical and experimental laboratory data. After the regional boundary of the CO<sub>2</sub> geological sequestration is determined, it can be optimized and CO<sub>2</sub> geological sequestration can be conducted in the areas that have favorable reservoir conditions, are relatively close to CO<sub>2</sub> emission sources, have a high degree of exploration, have an appropriate formation depth and have a small impact on the development of other mineral resources. The results show that (1) the areas suitable for the geological storage of CO<sub>2</sub> in the Ordos Basin are located in the distribution area of the Majiagou Formation in the Tianhuan Depression, except for the missing areas in the central paleo-uplift. The ares to the east of the Baiyanjing-Shajingzi fault, to the north of the northern margin of the Weibei uplift, to the west of the Yellow River fault, and to the south of the Yimeng uplift are suitable for CO<sub>2</sub> geological storage. (2) Based on the three aspects of technology, safety, and economic feasibility, it was determined that the Wushenqi-Jingbian-Yan'an karst slope area (I<sub>1</sub>) is the best CO<sub>2</sub> geological storage area, and the Yulin-Mizhi karst basin area (I<sub>2</sub>) is a favorable area for the geological storage of CO<sub>2</sub> in the Ordos Basin.</p><p> </p>